Master cylinder assemblies

Abstract

In a master cylinder assembly a booster valve assembly is adapted to control two separate supplies of booster fluid, and each supply is capable of advancing a modulator piston independently to operate a master cylinder.

I claim: 
     
       1. A master cylinder assembly for a vehicle hydraulic braking system comprising a housing having a first bore and a second bore, a modulator piston assembly working in said second bore, a master cylinder piston working in said first bore and adapted to be advanced in said first bore on advancement of the modulator piston assembly in said second bore, said housing being provided with a first pressure space defined in said first bore in front of said master cylinder piston, and with second, third, and fourth independent pressure spaces in said second bore and bounded by said modulator piston assembly, pressurisation of said second pressure space causing said modulator piston assembly to be urged rearwardly, whereas pressurisation of either of said third or fourth pressure spaces causing said modulator piston assembly to be urged forwardly, said housing being provided with a first inlet port for connecting said first pressure space to a fluid reservoir, with an outlet port leading from said first pressure space for connecting to a wheel brake, with a second inlet port leading into said second pressure space, and with third and fourth inlet ports leading respectively into said third and fourth pressure spaces, a normally open valve controlling communication between said first pressure space and said first inlet port and being adapted to close on forward movement of said master cylinder piston from its retracted position, said master cylinder assembly further comprising a dual booster valve assembly comprising first and second hydraulically separate booster valves, a single actuating member controlling both booster valves, said first booster valve being provided with a first booster valve inlet and a first booster valve outlet, said second booster valve being provided with a second booster valve inlet and a second booster valve outlet, said first and second booster valve inlets being connected to two separate supplies of pressure fluid, means connecting said first and second booster valve outlets independently to said third and fourth pressure spaces in said housing respectively, whereby on actuation of said actuating member pressure fluid is supplied to both said third and fourth pressure spaces when both of said pressure fluid supplies are operational, and is supplied to one of said third and fourth pressure spaces on failure of either of said supplies to advance the modulator piston assembly. 
     
     
       2. A master cylinder assembly as in claim 1 wherein said modulator piston assembly comprises a portion of larger diameter in front of a portion of smaller diameter, said third pressure space being defined behind said portion of smaller diameter, and said fourth pressure space being defined between a step in said second bore and said larger diameter portion. 
     
     
       3. A master cylinder assembly as in claim 1 wherein said actuating member of said dual booster valve assembly is pedal-operated, said booster valve assembly being remote from said housing. 
     
     
       4. A master cylinder as in claim 1 wherein there is at least two master cylinder pistons, and a modulator piston assembly is provided for each master cylinder piston. 
     
     
       5. A master cylinder assembly as in claim 1 including a third fluid pressure supply separate from said first and second supplies, and skid control means connected between said third supply and said second inlet port of said housing.